Diaphragm

ABSTRACT

An oil resistant diaphragm having a liquid contacting surface made of a vulcanized rubber composition of, or composed mainly of, partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber in which at least 50% of the conjugated diene units is hydrogenated. This diaphragm is superior in resistance to deteriorated gasoline and low temperature, and is suitable for the automobile fuel pump.

BACKGROUND OF THE INVENTION

The present invention relates to an oil resistant diaphragm having the liquid contact surface which is superior in resistance to deteriorated gasoline and low temperature. The diaphragm is suitable particularly for the fuel pump of the automobile fuel system.

The present-day automobile fuel system, especially the one equipped with an electronic fuel-injection system, needs a diaphragm that resists deteriorated gasoline resulting from the increased engine temperature and fuel pressure. The diaphragm should have the liquid contact surface which is resistant to the propagation of cracking caused by gasoline in contact at all times. In addition, the diaphragm has come to need low-temperature resistance with the spread of automobiles into cold districts. Heretofore, there has not been any diaphragm that meets all of such requirements.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an oil resistant diaphragm which is superior in resistance to deteriorated gasoline and low temperature.

It is another object of this invention to provide an oil resistant diaphragm which is superior in resistance to the propagation of cracks in addition to resistance to deteriorated gasoline and low temperature.

The above-mentioned performance is achieved by forming at least the liquid contact layer of the diaphragm with a vulcanized rubber composition of, or composed mainly of, partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber in which at least 50% of the conjugated diene units is hydrogenated.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view showing a diaphragm of this invention in which both surfaces are made of the same material.

FIG. 2 is a sectional view showing a diaphragm of this invention in which both surfaces are made of different materials.

DETAILED DESCRIPTION OF THE INVENTION

The both surfaces of the diaphragm 2A (FIG. 1) and the one surface L of the diaphragm 2B (FIG. 2) are made of a vulcanizate of partially hydrogenated unsaturated nitrile copolymer rubber (referred to as hydrogenated NBR) (A), or made of a vulcanizate of rubber composition (B), (C), or (D), (mentioned later) composed mainly of hydrogenated NBR.

(A) Hydrogenated NBR

Hydrogenated NBR is unsaturated nitrile-conjugated diene copolymer rubber produced by emulsion polymerization or solution polymerization, with at least 50% of the conjugated diene units hydrogenated. If the degree of hydrogenation is less than 50%, the properties such as resistance to deteriorated gasoline and low temperature are not improved as interded in this invention. 100% hydrogenation may be possible, but hydrogenation less than 98% is desirable for a proper cure rate in the case of sulfur valcanization. The degree of hydrogenation is estimated from iodine value.

The copolymer rubber to be hydrogenated is prepared by copolymerizing an unsaturated nitrile such as acrylonitrile and methacrylonitrile with at least one of conjugated dienes such as 1,3-butadiene, isoprene, and 1,3-pentadiene, or by copolymerizing the above-mentioned unsaturated nitrile with a conjugated diene partly substituted with an unsaturated carboxylic acid ester such as methyl ester, butyl ester, and 2-ethyl ester of acrylic acid, methacrylic acid, fumaric acid, or itaconic acid, or with N-methylol acrylamide. Examples of such copolymer rubbers include acrylonitrile-butadiene copolymer rubber, acrylonitrile-isoprene copolymer rubber, acrylonitrile-butadiene-isoprene copolymer rubber, acrylonitrile-butadiene-methyl acrylate copolymer rubber, and acrylonitrile-butadiene-butyl acrylate copolymer rubber. Most suitable among them is acrylonitrile-butadiene copolymer rubber (NBR).

The quantity of the unsaturated nitrile in the hydrogenated NBR is usually 10 to 70 wt %, and it is determined properly according to the object of use.

(B) A rubber compound composed of hydrogenated NBR (A) and polyvinyl chloride resin (referred to as PVC hereunder)

The PVC includes polyvinyl chloride and copolymers of vinyl chloride and vinyl acetate or other monoolefin monomers. The PVC is incorporated into the hydrogenated NBR in an amount greater than 5 wt %, preferably in an amount of about 20 wt % (inner percentage). If the quantity is less than 5 wt %, the effect of improving the resistance to deteriorated gasoline is not sufficient. The more is incorporated the PVC, the more is enhanced the resin-attributable properties. Thus, as a matter of course, there is a limit at which the rubber composition can be vulcanized but the properties of rubber are impaired. The quantity of PVC to be incorporated should be determined according to the intended use and required performance. The upper limit is usually 60 wt %. Incorporation of PVC into hydrogenated NBR is accomplished by mixing with a roll or Banbury mixer or by mixing in a solution, followed by coprecipitation and drying.

(C) A rubber compound composed of hydrogenated NBR (A) and liquid unsaturated nitrile-conjugated diene copolymer having a number-average molecular weight of 500 to 10,000 (referred to as liquid NBR hereunder).

For good miscibility with hydrogenated NBR and for improved properties intended in this invention, the liquid NBR is composed of 10 to 70 wt %, preferably 20 to 50 wt %, of unsaturated nitrile, 20 to 80 wt %, preferably 25 to 75 wt %, of conjugated diene, and 0 to 20 wt %, preferably 0.1 to 15 wt %, of vinyl monomer which is copolymerizable with unsaturated nitrile and conjugated diene. The unsaturated nitrile and conjugated diene are as mentioned under the paragraph for hydrogenated NBR. Preferable unsaturated nitrile is acrylonitrile and preferable conjugated diene is butadiene or isoprene. The vinyl monomer copolymerizable with the unsaturated nitrile and conjugated diene includes, for example, unsaturated carboxylic acid such as acrylic acid, methacrylic acid, and itaconic acid and esters thereof, vinyl pyridine monomer such as 2-vinylpyridine, and N-methylol acrylamide. Preferable among them are acrylic acid and methacrylic acid.

If the liquid NBR has a number-average molecular weight smaller than 500, the resulting rubber composition is easily attacked by solvent and poor in resistance to the propagation of cracks. On the other hand, if the number-average molecular weight exceeds 10,000, the effect of improving resistance to the propagation of cracks is not obtained. A preferable value is from 1000 to 5000. The liquid NBR is incorporated into the hydrogenated NBR in an amount greater than 2 wt %, (inner percentage). If the quantity is less than 2 wt %, the effect of liquid NBR is not sufficient. The upper limit is about 50 wt %, at which the resulting rubber composition is excessively low in viscosity and the physical properties such as permanent compression set become poor. Incorporation of liquid NBR into hydrogenated NBR may be accomplished in the same way as mentioned in the above paragraph (B).

(D) A rubber compound composed of hydrogenated NBR (A), liquid NBR, and PVC

The PVC and the quantity and method of its incorporation are as mentioned in the above paragraph (B). That is to say, the PVC includes polyvinyl chloride and copolymers of vinyl chloride and vinyl acetate or other monoolefin monomers. The PVC is incorporated into the composition composed of hydrogenated NBR and liquid NBR in an amount greater than 5 wt %, preferably in an amount of about 20 wt % (inner percentage).

The above-mentioned hydrogenated NBR (A), or the rubber compound (B), (C), or (D) composed mainly of hydrogenated NBR may be incorporated with commonly used auxiliary materials including inorganic fillers such as carbon black, silica, and metal oxide, organic fillers such as lignin, softener, plasticizer, antioxidant, and colorant, together with a proper amount of sulfur or peroxide vulcanizing agent. This rubber material is top coated on a substrate of nylon fibers, polyester fibers, or cotton with calender rolls, followed by punching in desired shape and dimensions and press molding, whereby the diaphragm is formed. The molding conditions are: die temperature 150° to 190° C., vulcanizing time 3 to 30 minutes, and molding pressure 50 to 150 kg/cm². One of the top coated layers which does not come into contact with liquid may be formed with NBR, CR, or CHR in place of hydrogenated NBR.

The invention is now described with reference to Examples and Comparative Examples.

The test pieces in Examples and Comparative Examples were prepared from the rubber materials compounded as shown in Table 1. The rubber material was calendered into a 2.0 mm thick sheet, which was then punched into a size of 75 mmφ and press-molded at 170° C. for 15 minutes under a load of 100 kgf/cm² (without substrate). Test pieces were punched out from this vulcanized diaphragm. The tests for properties were carried out according to the following methods. The results are shown in Tables 2 and 3.

(1) Dry physical properties

Measured according to JIS K-6301 (test pieces: dumbbell No. 3)

(2) Resistance to deteriorated gasoline

Test pieces were dipped in JIS fuel C containing 1 wt % of lauroyl peroxide at 70° C. (The length of the test piece was reduced to 6/10 in Examples 6 to 9 and Comparative Examples 4 and 5.) The fuel was renewed every 24 hours (1 cycle). At the end of the specified number of cycles, test pieces were measured for physical properties according to JIS K-6301 after drying at room temperature for 24 hours and further drying under reduced pressure at 60° C.

(3) Low-temperature resistance

The impact brittleness temperature was measured according to JIS K-6301.

(4) Heat aging resistance

Test pieces, dumbbell JIS No. 3, were measured for physical properties according to JIS K-6301 before and after heat aging at 120° C. for 70 hours (or 288 hours), and the rate of change as compared with the dry physical properties is expressed as ΔH_(S), ΔT_(B), and ΔE_(B) for break hardness, strength, and elongation at break, respectively.

(5) Resistance to propagation of cracks

A test piece, dumbbell JIS No. 1, with a 2 mm long crack made at the center of two marks 40 mm apart, was stretched 50% (so that the distance between the marks is increased to 60 mm) by a proper tool, and the stretched test piece was dipped in JIS fuel D at 40° C. The time for the test piece to break was measured.

(6) Gasoline resistance

A test piece measuring 20×20×2 mm was dipped in JIS fuel C at 40° C. for 48 hours, and the rate of change of the volume before and after dipping is shown.

(7) Gasohol resistance

A test piece measuring 20×20×2 mm was dipped in JIS fuel C containing 20 vol % of methanol at 40° C. for 48 hours, and the rate of change of the volume before and after dipping is shown.

It is to be noted from Table 2 that the diaphragm of this invention (Examples 1 to 5) outperforms that made of ordinary NBR (Comparative Examples 1 to 3) in resistance to deteriorated gasoline and low-temperature resistance and is in no way inferior in dry physical properties. The diaphragm made of PVC-containing hydrogenated NBR compound (Examples 2 to 5) are improved as compared with that made of hydrogenated NBR alone (Example 1) in dry physical properties.

It is to be noted from Table 3 that the diaphragms of this invention (Examples 6 to 9) are superior in resistance to deteriorated gasoline, resistance to propagation of cracks, low-temperature resistance, dry physical properties, and heat resistance. As compared with the diaphragm made of hydrogenated NBR alone (Example 1), the one made of hydrogenated NBR incorporated with liquid NBR (Examples 6 and 7) are superior in resistance to propagation of cracks. The incorporation of PVC further improves resistance to propagation of cracks.

                                      TABLE 1                                      __________________________________________________________________________                Example No.                 Comparative Example No.                            1   2  3  4  5  6  7  8  9  1   2  3  4  5                          __________________________________________________________________________     Composition of raw                                                             material rubber                                                                Hydrogenated NBR*.sup.1                                                                   100 95 90 85 70 90 80 80 70                                         NBR*.sup.2                             100 85 70                               NBR*.sup.3                                       90                            NBR*.sup.4                                          70                         Liquid NBR*.sup.5          10 20 5  5            10 5                          PVC*.sup.6     5  10 15 30       15 25     15 30    25                         MAF carbon black                                                                          30  28.5                                                                              27 25.5                                                                              21 45 45 30 25 50  45.5                                                                              41 60 40                         Plasticizer*.sup.7                                                                        20  23 24 25 27 25 25 30 30 20  25 27 25 30                         Stearic acid                                                                              1   1  1  1  1  1  1  1  1  1   1  1  1  1                          Zinc oxide (#3)                                                                           5   5  5  5  5  5  5  5  5  5   5  5  5  5                          Sulfur powder                                                                             0.5 0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5 0.5                                                                               0.5                                                                               0.5                                                                               0.5                        Vulcanization                                                                  accelerator                                                                    TET*.sup.8 2   2  2  2  2  2  2  2  2  2   2  2  2  2                          TMT*.sup.9 1   1  1  1  1  1  1  1  1  1   1  1  1  1                          MBT*.sup.10                                                                               0.5 0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5                                                                               0.5 0.5                                                                               0.5                                                                               0.5                                                                               0.5                        __________________________________________________________________________      Note to Table 1                                                                *.sup.1 Rate of hydrogenation: 90%                                             Quantity of acrylonitrile: 45 wt %                                             Viscosity ML.sub.1+4 (100° C.): 85                                      *.sup.2 Nipol DN101 (product of Nippon Zeon Co., Ltd.) containing 41 wt %      of acrylonitrile                                                               *.sup.3 Nipol DN101L (product of Nippon Zeon Co., Ltd.) containing 42 wt       of acrylonitrile                                                               *.sup.4 Nipol 1043J (product of Nippon Zeon Co., Ltd.) containing 29 wt %      of acrylonitrile                                                               *.sup.5 Nipol 1312J (product of Nippon Zeon Co., Ltd.)                         *.sup.6 Zeon 103 EP8 (product of Nippon Zeon Co., Ltd.)                        *.sup.7 Dibutoxyethoxyethyl adipate                                            *.sup.8 TET: tetraethylthiuram disulfide                                       *.sup.9 TMT: tetramethylthiuram monosulfide                                    *.sup.10 MBT: 2mercaptobenzothiazole                                     

                                      TABLE 2                                      __________________________________________________________________________                                    Comparative                                                     Example No.    Example No.                                     Test Items      1  2  3  4  5  1  2  3                                         __________________________________________________________________________     <Dry physical properties>                                                      H.sub.S (JIS A) 56 59 59 58 60 60 60 62                                        T.sub.B (kgf/cm.sup.2)                                                                         233                                                                               231                                                                               258                                                                               257                                                                               271                                                                               173                                                                               183                                                                               195                                       E.sub.B (%)     610                                                                               630                                                                               610                                                                               610                                                                               560                                                                               490                                                                               420                                                                               370                                       <Resistance to                                                                 deteriorated gasoline>                                                         T.sub.B (kgf/cm.sup.2)                                                                 0 cycle 253                                                                               259                                                                               276                                                                               274                                                                               284                                                                               179                                                                               190                                                                               201                                               2 cycles                                                                               210                                                                               221                                                                               236                                                                               250                                                                               236                                                                               74 80 91                                                8 cycles                                                                               161                                                                               176                                                                               181                                                                               190                                                                               138                                                                               40 49 62                                        E.sub.B (%)                                                                            0 cycle 590                                                                               600                                                                               570                                                                               570                                                                               520                                                                               470                                                                               410                                                                               370                                               2 cycles                                                                               470                                                                               460                                                                               450                                                                               430                                                                               410                                                                               60 60 50                                                8 cycles                                                                               300                                                                               300                                                                               310                                                                               320                                                                               300                                                                               40 40 30                                        E.sub.C (%)                                                                            0 cycle -- -- -- -- -- -- -- --                                                2 cycles                                                                               -- -- -- -- -- 30 30 40                                                8 cycles                                                                               240                                                                               250                                                                               250                                                                               250                                                                               260                                                                               10 10 10                                        <Low-temperature resistance>                                                   Impact brittleness                                                                             -49                                                                               -49                                                                               -47                                                                               -47                                                                               -47                                                                               -34                                                                               -35                                                                               -34                                       point (°C.)                                                             <Heat aging resistance>                                                        at 120° C. for 70 hours                                                 ΔH.sub.S (JIS A)                                                                         +6 +6 +7 +7 +7 +7 +8 +9                                        ΔT.sub.B (%)                                                                             +6 +10                                                                               +12                                                                               +2 -2 +10                                                                               +13                                                                               +19                                       ΔE.sub.B (%)                                                                             -15                                                                               -16                                                                               -20                                                                               -21                                                                               -12                                                                               -26                                                                               -39                                                                               -54                                       <Resistance to pro-                                                            pagation of cracks>                                                            Time to break (sec)                                                                            81 317                                                                               437                                                                               517                                                                               2084                                                                              90 270                                                                               420                                       <Gasoline resistance>                                                          Δ V (%)   20 18 16 15 10 18 16 13                                        <Gasohol resistance>                                                           Δ V (%)   47 44 42 39 32 45 40 36                                        __________________________________________________________________________      Note to Table 2                                                                .sup.(1) T.sub.B : Break strength                                              E.sub.B : Elongation at break                                                  H.sub.S : Hardness                                                             E.sub.C : Elongation to cause cracking                                         .sup.(2) "--" sign in E.sub.C indicates no cracking.                     

                  TABLE 3                                                          ______________________________________                                                                    Compara-                                                                       tive Ex-                                                         Example No.   ample No.                                           Test Items     6      7      8    9    4    5                                  ______________________________________                                         <Dry physical                                                                  properties>                                                                    T.sub.B (kgf/cm.sup.2)                                                                        213    168    232  263  130  102                                E.sub.B (%)    580    690    570  560  630  680                                H.sub.S (JIS A)                                                                               60     63     61   61   58   58                                 <Resistance to                                                                 deteriorated gasoline>                                                         T.sub.B (kgf/cm.sup.2)                                                                  1 cycle   194    153  219  193  44   87                                        2 cycles  180    144  229  191  45   63                                        4 cycles  162    128  232  158  37   40                               E.sub.B (%)                                                                             1 cycle   420    530  510  510  100  450                                       2 cycles  390    500  490  480  60   190                                       4 cycles  410    490  540  460  40   40                               E.sub.C (%)                                                                             1 cycle   --     --   --   --   60   330                                       2 cycles  --     --   --   --   40   110                                       4 cycles  370    450  --   420  10   30                               <Resistance to pro-                                                            pagation of cracks>                                                            Time to break (sec)                                                                           4480   9000   10.sup.6                                                                            10.sup.6                                                                            600  79                                                              up   up                                           <Heat aging resistance>                                                        at 120° C. for 70 hours                                                 ΔT.sub. B (%)                                                                           -2     -3     -1   -6   +26  +14                                ΔE.sub.B (%)                                                                            -27    -30    -19  -22  -43  -28                                ΔH.sub.S (JIS A)                                                                        +6     +7     +6   +7   +12  +13                                at 120° C. for 288 hours                                                ΔT.sub.B (%)                                                                            +8     +5     +3   ±0                                                                               +45  +24                                ΔE.sub.B (%)                                                                            -35    -48    -37  -54  -82  -79                                ΔH.sub.S (JIS A)                                                                        +14    +18    +16  +23  +32  +35                                <Low-temperature                                                               resistance>                                                                    Impact brittleness                                                                            -45    -48    -47  -53  -31  -40                                point (°C.)                                                             <Gasoline resistance>                                                          ΔV (%)   21     23     16   12   19   13                                 <Gasohol resistance>                                                           ΔV (%)   47     49     40   34   46   36                                 ______________________________________                                          Note to Table 3                                                                .sup.(1) T.sub.B : Break strength                                              E.sub.B : Elongation at break                                                  H.sub.S : Hardness                                                             E.sub.C : Elongation to cause cracking                                         .sup.(2) "--"  sign in E.sub.C indicates no cracking.                     

What is claimed is:
 1. A diaphragm having the liquid contacting surface made of a vulcanized rubber composition of partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber in which at least 50% of the conjugated diene units are hydrogenated, said copolymer rubber being incorporated with more than 2 wt % of liquid unsaturated nitrile-conjugated diene copolymer having a number-average molecular weight of 500 to 10,000.
 2. A diaphragm as claimed in claim 1, wherein the unsaturated nitrile-conjugated diene copolymer rubber to be hydrogenated contains 10 to 70 wt % of unsaturated nitrile, and the liquid unsaturated nitrile-conjugated diene copolymer is composed of 10 to 70 wt % of unsaturated nitrile, 20 to 80 wt % of conjugated diene, and 0 to 20 wt % of vinyl monomer copolymerizable with the unsaturated nitrile and conjugated diene.
 3. A diaphragm having the liquid contacting surface made of a vulcanized rubber composition of partially hydrogenated unsaturated nitrile-conjugated diene copolymer rubber in which at least 50% of the conjugated diene units are hydrogenated, said copolymer rubber being incorporated with more than 2 wt % of liquid unsaturated nitrile-conjugated diene copolymer having a number-average molecular weight of 500 to 10,000 and more than 5 wt % of polyvinyl chloride resin.
 4. A diaphragm as claimed in claim 3, wherein the unsaturated nitrile-conjugated diene copolymer rubber to be hydrogenated contains 10 to 70 wt % of unsaturated nitrile, and the liquid unsaturated nitrile-conjugated diene copolymer is composed of 10 to 70 wt % of unsaturated nitrile, 20 to 80 wt % of conjugated diene, and 0 to 20 wt % of vinyl monomer copolymerizable with the unsaturated nitrile and conjugated diene. 